1. Field of the Invention
This invention relates to a zoom lens for use with size of 35 mm, wherein a wide angle with an angle of field of 78.degree. is included in a magnification region therefor and which has a high magnification in which a zoom ratio is about 3.5 times.
2. Description of the Prior Art
In the past, as a zoom lens in which a wide angle is included in a magnification region therefor, a zoom lens for use with 35 mm size with an angle of field in the range of from 63.degree. to 34.degree. is known which comprises two groups of lenses. In the zoom lens of the type described, in order to secure aperture efficiency of the angle of field in the periphery without increasing an effective diameter of a lens of a first surface and when the first group of lenses are drawn out for focusing in order to prevent relative illumination even when focusing was made at close quarters, it is advantageous to provide an arrangement wherein a negative focal length is applied to the first group on the object side to make small an angle formed between the peripheral flux emitted from the first group and an optical axis. It is apparent however that so far as an image forming system is present in the case where the whole system is taken into consideration, a strong positive refractive power is required for the succeeding second group. Additionally, in order for the light flux which is subjected to emitting action of the first group in order to have a greater width, is incident upon the second group, a high degree of spherical aberration and coma aberration occurs on the side of a long focal length and it is difficult to restrain variation of aberrations over the entire zoom region. Therefore, the zoom ratio is in principal increased to a factor of two.
Recently, a zoom lens having more than three groups of lenses and having a high magnification with a wide angle included in a magnification region has been utilized. However, the leading zoom lens is of the semi-wide angle type in which the angle of field at the end of the short focal length is in the vicinity of 63.degree.. That is, the focal length is in the vicinity of 35 mm in case of 35 mm size. For a zoom lens in which the end of the short focal length is in the vicinity of 28 mm of the focal length and the zoom ratio is close to three times, Japanese Patent Publication No. 55-14403 disclosed a system in which a negative focal length is arranged in the first group. However, in this system, the overall length of the lens cannot be made short at the end of the short focal length and the slope of a cam curve is varied pronounced on the side of the short focal length, thereby adversely effecting operability in that portion. If the focal length of the first group is made small, it is advantageous to provide miniaturization and high magnification ratio, overcoming the aforesaid difficulties, whereas it is extremely difficult to correct aberrations, failing to provide high performance. A limit of the zoom ratio was up to three times by the reciprocal nature.